Solar Radiation Incident on the Surface

Hourly variation of solar radiation incident on various surfaces and the daily totals throughout the year at 40° latitude (from ASHRAE Handbook of Fundamentals, Ref. 1, Chap. 27, Table 15)

Solar radiation is radiant energy emitted by the sun, particularly electromagnetic energy. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum

Solar Radiation Incident on the Surface,* W/m2

Solar Time

Date

Direction
of
Surface

5

6

7

8

9

10

11

12
noon

13

14

15

16

17

18

19

Daily
Total

Jan.

N
NE
E
SE
S
SW
W
NW
Horizontal
Direct

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

20
63
402
483
271
20
20
20
51
446

43
47
557
811
579
48
43
43
198
753

66
66
448
875
771
185
59
59
348
865

68
68
222
803
884
428
68
68
448
912

71
71
76
647
922
647
76
71
482
926

68
68
68
428
884
803
222
68
448
912

66
59
59
185
771
875
448
66
348
865

43
43
43
48
579
811
557
47
198
753

20
20
20
20
271
483
402
63
51
446

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

446
489
1863
4266
5897
4266
1863
489
2568
—

Apr.

N
NE
E
SE
S
SW
W
NW
Horizontal
Direct

0
0
0
0
0
0
0
0
0
0

41
262
321
189
18
17
17
17
39
282

57
508
728
518
59
52
52
52
222
651

79
462
810
682
149
77
77
77
447
794

97
291
732
736
333
97
97
97
640
864

110
134
552
699
437
116
110
110
786
901

120
123
293
582
528
187
120
120
880
919

122
122
131
392
559
392
392
122
911
925

120
120
120
187
528
582
293
123
880
919

110
110
110
116
437
699
552
134
786
901

97
97
97
97
333
736
732
291
640
864

79
77
77
77
149
682
810
462
447
794

57
52
52
52
59
518
728
508
222
651

41
17
17
17
18
189
321
262
39
282

0
0
0
0
0
0
0
0
0
0

1117
2347
4006
4323
3536
4323
4006
2347
6938
—

July

N
NE
E
SE
S
SW
W
NW
Horizontal
Direct

3
8
7
2
0
0
0
0
1
7

133
454
498
248
39
39
39
39
115
434

109
590
739
460
76
71
71
71
320
656

103
540
782
580
108
95
95
95
528
762

117
383
701
617
190
114
114
114
702
818

126
203
531
576
292
131
126
126
838
850

134
144
294
460
369
155
134
134
922
866

138
138
149
291
395
291
149
138
949
871

134
134
134
155
369
460
294
144
922
866

126
126
126
131
292
576
531
203
838
850

117
114
114
114
190
617
701
383
702
818

103
95
95
95
108
580
782
540
528
762

109
71
71
71
76
460
739
590
320
656

133
39
39
39
39
248
498
454
115
434

3
0
0
0
0
2
7
8
1
7

1621
3068
4313
3849
2552
3849
4313
3068
3902
—

Oct.

N
NE
E
SE
S
SW
W
NW
Horizontal
Direct

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

7
74
163
152
44
7
7
7
14
152

40
178
626
680
321
40
40
40
156
643

62
84
652
853
547
66
62
62
351
811

77
80
505
864
711
137
87
87
509
884

87
87
256
770
813
364
87
87
608
917

90
90
97
599
847
599
97
90
640
927

87
87
87
364
813
770
256
87
608
917

77
87
87
137
711
864
505
80
509
884

62
62
62
66
547
853
652
84
351
811

40
40
40
40
321
680
626
178
156
643

7
7
7
7
44
152
163
74
14
152

0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0

453
869
2578
4543
5731
4543
2578
869
3917
—

*Multiply by 0.3171 to convert to Btu/h · ft2. Values given are for the 21st of the month for average days with no clouds. The values can be up to 15 percent higher at high elevations under very clear skies and up to 30 percent lower at very humid locations with very dusty industrial atmospheres. Daily totals are obtained using Simpson’s rule for integration with 10-min time intervals. Solar reflectance of the ground is assumed to be 0.2, which is valid for old concrete, crushed rock, and bright green grass. For a specified location, use solar radiation data obtained for that location. The direction of a surface indicates the direction a vertical surface is facing. For example, W represents the solar radiation incident on a west-facing wall per unit area of the wall. Solar time may deviate from the local time. Solar noon at a location is the time when the sun is at the highest location (and thus when the shadows are shortest). Solar radiation data are symmetric about the solar noon: the value on a west wall before the solar noon is equal to the value on an east wall two hours after the solar noon.